{"id":9210,"date":"2024-03-05T08:17:25","date_gmt":"2024-03-05T13:17:25","guid":{"rendered":"https:\/\/undecidedmf.com\/?p=9210"},"modified":"2024-03-15T16:08:21","modified_gmt":"2024-03-15T20:08:21","slug":"the-genius-of-hot-water-heat-pumps","status":"publish","type":"post","link":"https:\/\/undecidedmf.com\/the-genius-of-hot-water-heat-pumps\/","title":{"rendered":"The Genius Of Hot Water Heat Pumps"},"content":{"rendered":"

Today is a really hot topic: water heaters. No, it\u2019s not sexy, but water heater technology is kind of ingenious with its simplicity. A typical electric water heater has two heating elements; one near the bottom and one near the top, all housed in a very well insulated cylinder. As cold water is fed in near the bottom of the tank, the hot water is pushed out near the top. It\u2019s also pretty simple efficiency-wise. For each unit of electricity that\u2019s used, you get one unit of heat energy added to the water.<\/p>\n

However, my water heater is wearing one additional piece of technology on top \u2026 like a hat. It\u2019s a heat pump. That means for every unit of electricity I\u2019m spending I\u2019m getting 3 to 4 units of heat added to the water. It\u2019s way more efficient than any electric or natural gas water heater you can get, but hybrid heat pump water heaters have some quirks and challenges. Also, my setup is a little unique \u2026 like \u2026 what\u2019s that strange mini-me version of a water heater sitting next to it?<\/p>\n

I keep saying, \u201cheat pump all the things\u201d and I\u2019m not kidding. When it comes to energy efficiency you can\u2019t beat a technology that seems to break the laws of physics. Generating more heat energy than the amount of energy you put into it seems like a magic trick, but it\u2019s not. I\u2019ve got a 50 gallon Rheem Proterra hybrid water heater here. I\u2019ll be sharing my thoughts on this specific model as we go, but this is more about just using a heat pump water heater in general. Brand doesn\u2019t matter, but I\u2019ll be getting to the quicks and downsides in a bit.<\/p>\n

So why go with a heat pump water heater?<\/h2>\n

The biggest reason you\u2019d want a heat pump version is for exactly the reason I mentioned already. It\u2019s mostly about the Coefficient of Performance (COP). That\u2019s the ratio of energy in vs. energy out \u2026 or more simply how much heat energy you get for every kW of electricity or natural gas therms you put in. Just for clarity, because I\u2019ll be getting into comparing my old natural gas water heater to this new one, one therm is the energy content of about 100 cubic feet (2.83 cubic meters) of natural gas.1<\/a><\/sup><\/p>\n

The massive boost in COP is the big selling point of heat pumps in general. You\u2019ll be spending far less energy and money, in theory, to create hot water for your home. It\u2019s a very appealing sales pitch. However, this is where some of the downsides start to creep in, or at least the perception issues start to creep in.<\/p>\n

What about the downsides?<\/h2>\n

The first potential pitfall is the cost. Heat pump hybrid models are just more expensive than straight electric or natural gas models. In my old house, we had a 40 gallon natural gas model that cost about $800, not including installation. The Rheem I have now retails for around $1,500 plus installation, so there\u2019s a sizable jump in cost. However, there are rebates and incentives available in most places to help knock that cost down. Sometimes those rebates come from the state or your local utility company, so it\u2019s best to do your due diligence before you make a purchase. In my case, here in Massachusetts, there\u2019s the MassSave program which will cover $750 of that cost.2<\/a><\/sup> The best part about that one is that it\u2019s usually available as an instant rebate when you buy the water heater. So, suddenly that $1,500 is now $750. There\u2019s also a federal tax credit of up to 30% (which is capped at $2,000) off the full installation (after local rebates have been applied). So if the total including installation was $2,500, here in Massachusetts you\u2019d end up paying about $1,225 (eg. original cost: $2,500 – $750 in state rebates – $525 in Federal incentives). Bottom line: in some cases it can be equal to or cheaper than a standard water heater depending on what rebates are available in your area.<\/p>\n

<\/p>\n

The other couple of common elements that I see brought up a lot are: noise and recovery time. When it comes to the noise issue, your mileage will vary wildly by brand, model, and sometimes the luck of the draw. In my case, I haven\u2019t noticed any significant noise issues at all<\/em>. I have an insulated mechanical room that\u2019s not too far from the main living room area and I never hear the water heater running. However, I do hear my HVAC system ramping up and down. I have heard from others that they\u2019ve had some noise issues with this exact model of water heater, so be aware. A friend of the channel, Paul Braren, has some great articles on his website about this.<\/p>\n

As for recovery time, which is a measure of how quickly it can heat cold water back up, it\u2019s also been a non-issue for me. In fact, I\u2019d argue that this is largely a myth that heat pump water heaters have a slow recovery time. It\u2019s going to depend on how much hot water you use and what settings you have on your water heater. For this Rheem, there are a few different modes you can put it in: Energy Saver, Heat Pump, and High Demand. Energy Saver is the default and what I\u2019ve been using. On this setting, it fully utilizes the heat pump compressor for the best COP possible, but also incorporates the electric heating elements for high demand and recovery needs. It\u2019s a balanced approach. The other two modes are what you\u2019d expect. \u201cHeat Pump\u201d is full on heat pump only, which can affect the recovery time and can even increase energy consumption, according to Rheem. \u201cHigh Demand\u201d mode puts more emphasis on the electric elements and also increases energy consumption. I\u2019ll get into what I\u2019m actually seeing in just a minute.<\/p>\n

The final potential pitfall of a heat pump water heater is space \u2026 and I mean physical space. Because they have an air source heat pump strapped to the top, like a hat, they need a certain air volume in the room they occupy. The way the heat pump works is that it passes the room\u2019s air through a heat exchanger to extract the heat into a working fluid. That fluid is then sent through a compressor and turned into vapor, which circulates through pipes snaking around the water heater, making hot water. As the heat is extracted back out of the working fluid it cools off, turning back into a liquid, and ready to repeat the cycle. The side effect is that the air that\u2019s getting ejected from the heat exchanger is cool and dry. If the room\u2019s volume is too small, the heat pump will lose efficiency as all the usable heat is extracted from the room\u2019s air.<\/p>\n

This is VERY noticeable in my setup. My mechanical room is technically too small. You need about 700 cubic feet, but my mechanical room is only about 600 cubic feet \u2026 and that doesn\u2019t account for all the equipment inside it taking up space. It\u2019s probably closer to 450-500 cubic feet. When we first moved into the house, the mechanical room felt like a meat locker when you opened the door: in other words, very cold. There are ways you can vent the water heater to alleviate this issue, but we opted to not do that \u2026 at least not yet.<\/p>\n

The reason? That little mini-me tank sitting next to the Rheem is why. I have my water heater tied into my geothermal HVAC system that\u2019s heating and cooling my entire house. The excess heat from that system\u2019s compressor is captured into water that sits in that tank waiting to be used by the Rheem water heater. That means our Rheem isn\u2019t refilling itself with cold water straight from the outside \u2014 it\u2019s refilling with water that is probably already over 110F. I really want to wire a sensor into the holding tank to track the water temp, but haven\u2019t gotten around to it yet. Anyway, the end result is that my water heater doesn\u2019t have to work as hard to get my water up to temp.<\/p>\n

We didn\u2019t get the geothermal desuperheater hooked up and working until we\u2019d been living here for almost two months. After we did, I noticed that the mechanical room isn\u2019t meat-locker cold anymore, but it\u2019s still cool \u2026 which is cool.<\/p>\n

What\u2019s the reality so far?<\/h2>\n

That leads me right into the performance I\u2019ve been seeing. So strap on your nerd hardhat, because I\u2019m about to drop some numbers and charts right on your head. At this point I still don\u2019t have a ton of data, but enough to start getting a sense of where this is going. Since we didn\u2019t move in until August, I\u2019m only looking at September through January and comparing this to the same months last year with our old natural gas water heater. If you\u2019re curious, I had an Aquanta smart device installed on my water heater that tracked exactly how much gas we were using.<\/p>\n

\"Gas

Gas Therms converted to kWh vs. Heat Pump kWh<\/p><\/div>\n

<\/figure>\n
<\/figure>\n

For this first chart it\u2019s the amount of gas vs. amount of electricity. You\u2019ll notice that there\u2019s a noticeable jump in October for both gas and electric because that\u2019s when the cold weather really kicks in. December through February tend to be the highest use case months, so there\u2019s another uptick noticeable for gas in December. What\u2019s interesting though is that you can see our electricity didn\u2019t jump in December. In fact, it\u2019s slowly been declining each month since October. My hunch right now is that it\u2019s because of the geothermal holding tank, which started up in October. It counteracted the typical increase.<\/p>\n

Operational costs are another story though.<\/p>\n

\"Gas

Gas vs. Heat Pump – My Costs<\/p><\/div>\n

<\/figure>\n

If you look at this chart, you\u2019ll notice that gas and electricity are basically a wash in September and December, but electricity is dramatically higher in October and November. The reason? Gas and electricity prices in my area. Electricity in Massachusetts is very high. In fact, we boast some of the highest in the country. We\u2019re paying around $0.30\/kWh vs. gas which was coming in around $2.18\/therm (at the time we were using it). The cost benefit is kind of a mixed bag in my area. Massachusetts electricity and gas prices mean this costs me about 22% more for hybrid heat pump hot water based on the limited data I have. I have a hunch that will change over the coming months because we\u2019re still experimenting to find the best settings for us. We may still try venting the water heater, so it has more air to draw from. However, if you look at the national average cost of electricity ($0.17\/kWh) and gas ($1.66\/therm) and apply it to my usage, it\u2019s a different story.<\/p>\n

\"Gas

Gas vs. Heat Pump – National Averages<\/p><\/div>\n

<\/figure>\n

Electricity wins hands down across the board. Nationally it would cost almost 21% less to go with an electric heat pump water heater. Again \u2026 based on only a few months of my personal data.<\/p>\n

I also have solar on my house, which is currently trending towards my goal of net zero energy from the grid over the course of a year. If that plays out, the actual cost of electricity to generate my hot water will be zero, which isn\u2019t possible with natural gas.<\/p>\n

Is it worth it to go with a heat pump water heater? Yes, in the vast majority of cases, it\u2019s absolutely the best option out there. However, as you can see in my current data, it\u2019s not completely cut and dry depending on what your electricity and natural gas prices are. If you\u2019re already using a standard electric water heater, it\u2019s a no-brainer to go heat pump. Again, upfront costs really aren\u2019t that different right now with all the rebates available from utilities, state and federal rebates. In some cases, it can be cheaper to install a heat pump water heater \u2026 and then the long term benefits after that.<\/p>\n

<\/p>\n

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  1. Wikipedia – Therm<\/a> \u21a9\ufe0e<\/a><\/li>\n
  2. MassSave Rebate Program<\/a> \u21a9\ufe0e<\/a><\/li>\n<\/ol>\n<\/div>","protected":false},"excerpt":{"rendered":"

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